CODEWITHSUNDEEP
hadoopmapreduce
CodeReaper
CodeReaper

Reputation: 387

RDBMS VS MAP REDUCE

I was going through Hadoop- The definitive Guide and i came across these lines:

Normalization poses problems for MapReduce, since it makes reading a record a nonlocal operation, and one of the central assumptions that MapReduce makes is that it is possible to perform (high-speed) streaming reads and writes.

Can someone explain what do these lines actually mean in layman language?

I know what is Normalization. How does it make makes reading a record a nonlocal operation? What is the meaning of a non local operation in reference to hadoop?

Upvotes: 3

Views: 839

Answers (1)

user1743173
user1743173

Reputation:

In hadoop a local operation refers to executing code in the same physical location where the data it needs to work with is being stored.

When you normalize your data you're essentially splitting it up. If this "split up" data gets distributed in 2 physically different areas you suddenly have non-local operations.

Upvotes: 5

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